Pump nozzle of a type with an open injection nozzle

ABSTRACT

A unit fuel injector of the type with an open injector comprises an injector body ( 1 ) with an axial space ( 4 ), which ends in an injector cap ( 3 ), an injection plunger ( 15 ) guided in the axial space and serving as a closing-off element, which injection plunger forms in the axial space a pressure space ( 23 ) from which the injection bores ( 60, 61 ) of an upper row ( 60 ) and a lower row ( 61 ) extend. To allow the injector cross section to be adapted to all operating states, the injection plunger ( 15 ) has an axial bore ( 30 ), in which a coaxial plunger needle ( 31 ) is guided in the longitudinal direction of the injector, the needle part ( 32 ) of which needle interacts with a seat ( 62 ) formed by the interior of the injector cap ( 3 ) and arranged beneath the upper row of injection bores ( 60 ), and above the plunger part ( 32 ) of the plunger needle ( 31 ) there is provided a compression spring ( 35 ) acting on it in a downward direction, and the plunger needle forms beneath its plunger part ( 32 ) in the axial bore ( 30 ) a control chamber ( 50 ), which can be fed by a control medium which raises the plunger needle ( 31 ) against the force of the compression spring ( 35 ) with respect to the injection plunger ( 15 ).

BACKGROUND OF THE INVENTION

The invention relates to a unit fuel injector of the type with an openinjector, comprising an injector body with an axial space, which ends inan injector cap with injection bores, comprising an injection plungerguided in the axial space and serving as a closing-off element, whichinjection plunger bounds in the axial space a pressure space from whichthe injection bores extend.

A unit fuel injector of the type with an open injector is known, forexample, from EP 460 693 A1. It has the special feature that theinjection plunger is a pumping element and closing element at the sametime. These unit fuel injectors also have the problem when they are usedin high-power diesel engines—which are usually supercharged—with respectto the minimizing of consumption and emissions that the injectionrequirements differ considerably between idling and full load.

During idling and at low compression pressure, the rate of injection islow and the ignition delay is long. During the ignition delay, as littlefuel as possible is to be injected as slowly as possible, andnevertheless atomized well. At full load and a high engine speed, on theother hand, the rate of injection is great—in the case of superchargedhigh-power engines even particularly great—and the duration of injectionis to be as short as possible, since only a limited crank angle is ofcourse available for the injection. All in all, optimizing combustionwith regard to consumption and emissions requires a uniform distributionof the fuel in the combustion chamber and defined atomization.

The greater the differences in rates and speeds, the more difficult itis to optimize combustion with constant injector cross sections.Although it is known from EP 470 348 A1 and DE 44 32 686 C2 to provide anumber of rows of injection bores and two concentric plunger needles inunit fuel injectors, in which the pumping element and closing elementare separate, in order in this way to be able to adapt the cross sectionof the injector to the operating state, these solutions concern only thevalve function and consequently cannot be transferred to the open unitfuel injectors of the generic type. Due to their special structuraldesign, there is a different relationship between the cross section ofthe injector and the injection pressure.

SUMMARY OF THE INVENTION

The invention is therefore based on the object of being able to adaptthe cross section of the injector and the delivery rate to therespective operating state even in the case of unit fuel injectors ofthe generic type. Adaptation is to be understood here as meaning boththe control during operation and the design.

This is achieved according to the invention by the features that

a) the injector cap (3) has a first group (60) and a second group (61)of injection bores (60, 61), of which the first group (60) is assignedto the injection plunger (15) and the second group (61) can be closedoff separately from the first,

b) the injection plunger (15) has an axial bore (30), in which a plungerneedle (31) is guided, the needle part of which interacts with a seat(21; 62; 72) formed in the interior of the injector cap (3), the secondgroup of injection bores (61) being assigned to the plunger needle (31),

c) the plunger needle (31) has a plunger part (32) on which acompression spring (35) acts in a downward direction and which bounds acontrol chamber (50) in the axial bore (30),

d) the control chamber (50) can be fed a control medium, which raisesthe plunger needle (31) against the force of the compression spring (35)with respect to the injection plunger (15), so that said needle followsthe movement of said plunger.

The two groups of injection bores can be closed off separately, thefirst by the injection plunger, the second by the plunger needle, whichin certain load states also acts as the injection plunger. In thesestates, not only the injector cross section but also the pumpcharacteristics are changed. This is possible only because both closingelements are pumping elements.

During idling and at low load, the plunger needle remains closed. As aresult, in this operating state the volume of the delivery space isinitially small. Furthermore, the effective area of the injectionplunger is only that of a circular ring and is therefore smaller, whichmeans a relatively higher injection pressure, in particular duringhydrostatic pressure transmission from the pump drive to the injectionplunger. Finally, the injector cross section is only the sum of thecross sections of the one row of injection bores. The injection boresmay be relatively small, in order to achieve a long duration ofinjection. This makes the injection pressure high, which improves theatomization of the fuel.

At higher part load or full load and a high engine speed, the plungerneedle is drawn into the injection plunger. As a result, the injectionbores of the further row are also open, thereby increasing the availablecross section of the injection bores. Furthermore, the volume of thedelivery space and the plunger area—now comprising the area of theinjection plunger and the needle—is greater. This means a considerablygreater delivery rate per unit of time at the same engine speed. Thereis consequently a threefold effect.

All this is achieved with relatively low additional technical outlay.What is more, the control is also not sophisticated, since it only needstwo positions of the plunger needle. Consequently, exact positioning ofa final control element is not required. The engine controller only hasto be provided with a threshold value or a curve in the characteristicmap, at which value or curve a switch is made from one mode to theother. All in all, it is possible in this way to adjust both thedelivery rate and the effective injector cross sections, evenindependently of each other.

In an advantageous design, the feeding of the control medium to thecontrol chamber takes place through a feeding bore in the injector bodyand a branch bore in the injection plunger, with a longitudinal groovebeing provided in the injector body or in the injection plunger.Consequently, the problem of continuously varying the pressure in thecontrol chamber moving with the injection plunger is elegantly solved.

A further simplification is obtained if the injection plunger has a stopfixing the uppermost position of the plunger needle. As a result,vibrations of the plunger needle are avoided and the control pressuredoes not need to be maintained exactly. As a result, the unit fuelinjector is insensitive to pressure losses in the event of wear.

In an advantageous development, the injection plunger has at its outerwall an annular space, which connects the fuel feed to a return flowwhen the injection plunger is closed. As a result, once injection hasbeen completed the excess pressure in the fuel feed line can be relievedand flushing and cooling can be carried out at the same time, withoutcolliding with the feed of control medium.

To allow the entire engine characteristic map to be covered optimallyand the limits between the two ranges to be chosen optimally, it hasproven to be advantageous to choose the ratio of the diameters of theinjection plunger and needle part of the plunger needle to be in therange between 1:2 and 1:3, the diameter of the first group of injectionbores to be less than that of the second group of injection bores, andthe ratio of the cross section of all the injection bores of the firstgroup to that of all the injection bores of the second group to begreater than the ratio of the effective cross sections of the injectionplunger and injection needle.

The shape and design of the closing elements, as well as the groupingand arrangement of the injection bores, may vary considerably within thescope of the invention and be adapted to the requirements of the pumpingfunction. A particularly advantageous solution is that the injector caphas on the inside a conical seat and the second group of injection boresis arranged beneath the first group of injection bores, the groups ofinjection bores respectively beginning at the same height.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is described and explained below on the basis ofillustrations of a preferred exemplary embodiment. In the figures:

FIG. 1 shows the pumping injector in a first operating position,

FIG. 2 shows the same, in a second operating position,

FIG. 3 shows a cross section along III—III in FIG. 2,

FIG. 4 shows the same, in a third working position,

FIG. 5 shows a cross section along V—V in FIG. 4,

FIG. 6 shows a longitudinal section along VI—VI in FIG. 4,

FIG. 7 shows detail A in FIG. 1, enlarged, and

FIG. 8 shows a variant of detail A in FIG. 1, enlarged.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

In FIG. 1, the entire injector body is denoted in a summarizing way by1. It may be composed of one or more parts; in the present example it isdivided along its radial surface 2 for production reasons. At thebottom, it goes over into an injector cap 3 and contains over its entirelength an axial space 4 which is accessible from the top. This spacebegins at the top with a bore 5, which is interrupted at a shoulder-likeconstriction 6 and further down forms a first cylindrical bore 8 and asmaller second cylindrical bore 9.

Right at the top in the interior of the axial space 4, a drive plungeris guided in a sealed and movable manner; it is driven for example by acamshaft (not represented). This is followed by an intermediate plunger11, which together with the drive plunger forms an injection-adjustingspace 12, which leads via a connecting bore 13 to theinjection-adjusting control (not represented). 14 denotes an onlyindicated return flow, which connects the axial space 4 to the returnflow of the injection system.

The intermediate plunger 11 acts on an injection plunger 15. At the top,it has a collar 16, on which there acts from below a restoring spring17, designed as a compression spring, the lower end of which issupported on the constriction 6. The injection plunger 15 isconsequently pressed in an upward direction by the restoring spring 17,a stop bead 18 bearing against the constriction 6 when at rest. Furtherbelow, the injection plunger 15 fits into the first cylindrical bore 8,which reaches in a downward direction from a shoulder 7, then fits intothe smaller second cylindrical bore 9 and ends with an end cone 20. Atthe end of the injection, the end cone 20 rests on a seating cone 21 ofthe injector cap. Between the injection plunger 15, the firstcylindrical bore 8 and a pressure shoulder 19 of the injection plunger15 there is formed a metering space 22 and further below, between thesecond cylindrical bore 9, the end cone 20 and the seating cone 21,there is formed a pressure space 23. At 24, fuel is introduced at thepressure of a delivery pump (not represented) into the injector body 1and passes via a longitudinal bore 25 and a feed opening 26 into themetering space 22. From the latter, it flows during the injectionthrough a narrow annular passage 27 into the pressure space 23 and fromthere via injection bores into the combustion chamber of the engine.Provided in the injector body 1 is an inwardly protruding anti-twistingpin 28, which interacts with a vertical guiding groove 29 on theinjection plunger 15.

In the injection plunger 15 there is then an axial bore 30, in which aplunger needle 31 is guided in the longitudinal direction. It comprisesan upper plunger part 32 and a lower needle part 33. On the plunger part32 there rests a small pressure plate 34, on which a compression spring35 acts in a downward direction. The upper end of said spring issupported on a plug 36, which is pressed or screwed into the injectionplunger 15. The plug 36 has an axial pressure-equalizing bore 37 andforms a stop 38 when the small pressure plate 34 is raised—as still tobe described.

In FIG. 2 it can be seen better that a control chamber 50 is formedbetween the plunger part 32 and the axial bore 30. Control medium is fedto the injector body 1 via an opening 40 (see FIG. 6) and passes via afeed bore 41 in the injector body 1 into the central space and fromthere directly or—depending on the position of the injection plunger—viaa longitudinal groove 42, which may be machined both into the injectionplunger 15 and into the inner wall of the injector body, through abranch bore 43 into the control chamber 50.

In FIG. 3 it can be seen that the injection plunger 15 has at a certainheight and over part of its circumference a milled relief, which formsan annular space 52. This establishes the connection between a flushingbore 53 and a flushing channel 54, which leads into the axial space 4.The latter is connected to the return flow 14.

In FIG. 7, the lower end of the injector cap is shown enlarged. It hasan upper row of injection bores 60 and a lower row of injection bores61, which are arranged at a certain distance from one another. Theinjection bores may, within the scope of the invention, be designed verydifferently with regard to arrangement, length, cross section and entry.Formed between the injection bores of the two rows 60, 61 is a seat 62,on which a cone 63 of the needle part 33 rests. The transition to thecone 63 takes place at an edge 64, which lies somewhat higher than theentry of the injection bores of the upper row when the plunger needle isclosed. To protect the injection bores and for machining reasons, theparts of the seating cone 21 in which the injection bores open out havebeen withdrawn, approximately at 65. In another embodiment according toFIG. 8, seating-hole-drilled injection bores 70, 71 have been made,extending from a common seat 72.

The operating mode is now explained with reference to FIGS. 1, 2 and 4:

FIG. 1 shows the unit fuel injector after a completed metering stroke,at the end of the upward movement of the injection plunger 15 for idlingor low load. In this operating state, the control chamber 50 ispressureless, for which reason the plunger needle 31 has not taken partin the upward movement of the injection plunger; in spite of theupward-moving injection plunger 15, it has been kept closed by thecompression spring 35. If the injection plunger 15 is then moved in adownward direction into the position shown in FIG. 2, the fuel isinjected from the pressure shoulder 19 out of the metering space 22through the annular passage 27 into the pressure space 23 and from thereonly from the end cone 20 of the injection plunger through the injectionbores 60 of the upper row into the combustion chamber of the engine. Ifthe control chamber 50 continues to remain pressureless, the injectionplunger is moved in an upward direction again on its own, back into theposition of FIG. 1, leaving the plunger needle 13 behind in the closedposition.

If, however, control pressure is applied via the feed line 40, 41, thispressure passes via the bores 41, 43, in every position of the injectionplunger 15 because of the longitudinal groove 42, into the controlchamber 50. This exerts an upwardly directed force onto the plunger part32 of the plunger needle 31. If the injection plunger 15 is then movedin an upward direction, the pressure of the control medium in thecontrol chamber 50 overcomes the force of the compression spring 35 andthe plunger needle 31 moves in an upward direction with the injectionplunger 15. This position is shown in FIG. 3. Since the plunger needlehas now also been drawn in, the volume of the pressure space 23 isgreater, as is the common area of the injection plunger and plungerneedle. If both are then moved in a downward direction (the plunger areais consequently greater), the injection takes place through theinjection bores 60, 61 of both rows. In this case, the rate may also begreater, if so desired by the rate control.

By coordinating the effective areas of the injection plunger and plungerneedle—a ratio in the range specified is advantageous—and thecross-sectional areas of the injection bores 60, 61 of the two rows, thespray pattern and course of combustion can be optimized. At low load,injection takes place only through the injection bores 60 of the upperrow, for which reason their diameter may be smaller than that of thelower row 61. For optimum coordination, furthermore, the ratio of thecross section of all the injection bores (60) of the upper row to thatof all the injection bores of the lower row (61) may be greater than theratio of the effective cross sections of the injection plunger (15) andplunger needle.

What is claimed is:
 1. A unit fuel injector of the type with an openinjector having a pump and an injector in the unit, comprising aninjector body (1) with an axial space (4), which ends in an injector cap(3) with injection bores, comprising an injection plunger (15) guided inthe axial space and serving as a closing-off element, which injectionplunger bounds in the axial space a pressure space (23) from which theinjection bores extend, wherein a) the injector cap (3) has a firstgroup (60) and a second group (61) of injection bores (60, 61), of whichthe first group (60) is associated with the injection plunger (15) andthe second group (61) can be closed off separately from the first, b)the injection plunger (15) has an axial bore (30), in which a plungerneedle (31) is guided, a needle part of which interacts with a seat (21;62; 72) formed in the interior of the injector cap (3), the second groupof injection bores (61) is associated with the plunger needle (31), c)the plunger needle (31) has a plunger part (32) or which a compressionspring (35) acts in a downward direction and which defines a controlchamber (50) in the axial bore (30), d) the control chamber (50) is feda control medium indicating load, which raises the plunger needle (131)against the force of the compression spring (35) with respect to theinjection plunger (15), so that said needle follows the movement of saidplunger.
 2. The unit fuel injector as claimed in claim 1, wherein thefeeding of the control medium to the control chamber (50) takes placethrough a feeding bore (41) in the injector body (1) and a branch bore(43) in the injection plunger (15), with a longitudinal groove (42)being provided in the injector body (1) or in the injection plunger(15).
 3. The unit fuel injector as claimed in claim 1, wherein theinjection plunger (15) has a stop (38) fixing the uppermost position ofthe plunger needle (31).
 4. The unit fuel injector as claimed in claim1, wherein the injection plunger (15) has at its outer wall an annularspace, which connects a fuel feed (24) to a return flow (14) when theinjection plunger is closed.
 5. The unit fuel injector as claimed inclaim 1, wherein the ratio of the diameters of the injection plunger(15) and needle part (33) of the plunger needle (31) is in the rangebetween 1:2 and 1:3.5.
 6. The unit fuel injector as claimed in claim 1,wherein the diameter of the first group of injection bores (60) is lessthan that of the second group of injection bores (61).
 7. The unit fuelinjector as claimed in claim 1, wherein the ratio of the cross sectionof all the injection bores (60) of the first group to that of all theinjection bores of the second group (61) is greater than the ratio ofthe effective cross sections of the injection plunger (15) and plungerneedle (31).
 8. The unit fuel injector as claimed in claim 1, whereinthe injector cap (3) has on the inside a conical seat (21) and thesecond group (61) of injection bores (61) is arranged beneath the firstgroup (60) of injection bores (60), the groups of injection bores (60,61) respectively beginning at the same height.
 9. The unit fuel injectoras claimed in claim 8, wherein in the interior of the injector cap (3)there is formed the seat (21) for the injection plunger (15) and a seat(62) for the plunger needle (31), the first group of injection bores(60) being arranged beneath the seat of the injection plunger (21). 10.The unit fuel injector as claimed in claim 8, wherein in the interior ofthe injector cap (3) there is provided the seat (21) for the injectionplunger (15) and for the plunger needle (31), from which at least one ofthe groups of injection bores (70, 71) extends.